This invention relates to current based power supplies and particularly to an improved supply operable from a wide range current source taken from an AC power line. The power supply of this invention includes a multi-stage energy storage system capable of very fast turn-on speeds and operation over a wide range of input supply current levels.
In monitoring the operating function of high voltage power supply lines (EHV) and for other purposes requiring equipment electrical power at locations remote from usual power sources there is needed a remotely locatable electric power supply to provide voltage regulated power at low levels for electronic equipment. Such a power supply should be capable of being operated by magnetic (transformer) coupling to the power supply lines themselves using the line current exclusively as a power source. It is desired that the power supply have a start-up time (from a fully de-energized condition to full regulation) following an initiation signal, such as a current zero crossing relating to breaker close, of extremely short timing, for example, less than 150 microseconds at a current magnitude of approximately 4.0 per unit (p.u.) (where 1 p.u.=rated line current). The power supply should be able to maintain full regulation during its operation over an input current range of from 0.02 p.u. to over 40 p.u. where 1 p.u. of current depending upon the line given, may vary from a few hundred amperes to a few thousand amperes. Aside from the wide range of current input and high turn-on speed requirements, the power supply should also be efficient and of a highly reliable design. Heretofore, a power supply meeting the foregoing requirements has not been available.
Heretofore, current transformers used in supplies proposed for the purpose of monitoring EHV power lines have been of the saturable type in which initial power delivered by the power supply may not be established for a full half cycle after initial breaker opening, particularly if the initial line current has the same polarity as the current by which the transformer becomes saturated prior to breaker opening.